The present invention relates to a sealed beam type reflective lamp and, more particularly, to an improvement in a front lens of an envelope of a sealed beam type reflective lamp having reflective lighting characteristics of spot lighting type.
A sealed beam type reflective lamp comprises a reflector on the inner surface of which is deposited a metal reflective film of aluminum or the like, a light source assembly having a tungsten coil filament arranged near the central axis of the reflector, and a front lens sealed to the opening of the reflector. Sealed beam type reflective lamps are classified into those of spot lighting type and those of flood lighting type according to the size of the illuminating area. With a sealed beam type reflective lamp of spot lighting type, a beam spread exhibiting a luminous intensity of 1/2 the central luminous intensity is 15.degree.. The deviation of the luminous intensity at the illuminating area is required to be small. As a typical example of such a lamp, a lamp of 100 V-100 W is known which has an envelope having a diameter of about 121 mm (1/8".times.38).
In a conventional sealed beam type reflective lamp of spot lighting type, the inner surface of the front lens is stippled to disperse incident light. A front lens having such stipples has an unsatisfactory converging effect. In order to increase the central luminous intensity and to improve the converging effect, the tungsten coil filament is brought closer to the stippled front lens, the beam spread exhibiting a luminous intensity of 1/2 the central luminous intensity exceeds 15.degree., the central luminous intensity is lowered, and the deviation of the luminous intensity at the illuminating area increases. These characteristics are not preferable for a lamp of spot lighting type.